1. Field of the Invention
The present invention relates to light-stable coating compositions containing a mixture of at least two mutually compatible cosolvent-free, aqueous, anionic dispersions A and B of polyurethane polyureas.
The present invention also relates to recyclable strippable coating compositions consisting of at least two different cosolvent-free, aqueous, anionic dispersions A and B of polyurethane polyureas, a process for their production and their use as coating compositions, preferably as strippable coating compositions for the temporary protection of motor vehicles, aircraft, steel and aluminium profiles, glass and plastics discs and arbitrary other substrates, and processes for the recovery of the used stripped coating layers.
2. Description of the Prior Art
Anionic polyurethane polyurea dispersions are known. Cosolvent-free, aqueous, anionic polyurethane dispersions, processes for their production and their use as coating compositions, coating agents, adhesives and strippable coating compositions are also known. DE-A 19 653 585, describes polyurea dispersions which after physical drying at 20xc2x0 to 100xc2x0 C., preferably at 20xc2x0 to 80xc2x0 C., provide transparent, high-gloss UV-resistant, temperature-resistant (xe2x88x9230xc2x0 to 80xc2x0 C.) coatings that are resistant to precipitations (of an organic or inorganic nature), and that on the one hand bond well to substrates and on the other hand can easily be removed by stripping. The tear strength and elongation of the coatings layers are appropriately high. A coatings dispersion that can be obtained according to DE-A 19 653 585 is denoted hereinafter as dispersion A.
Mixtures of polyolefins used as strippable coating compositions for automobiles are known from WO 98/23692. However these mixtures do not contain any polyurethane (PUR) constituents. The strippable coatings described therein are also not recyclable.
There is a need for a higher hardness and lower elongation of the polyurethane ureas A used as recyclable strippable coating compositions.
Accordingly, an object of the present invention is to provide new aqueous anionic polyurethane polymers that can be used without any problem and in an environmentally friendly manner and that produce coating compositions and coatings that satisfy requirements with regard to mechanical properties, weathering, light-resistance, transparency, temperature resistance, strippability, water resistance, resistance to precipitations (of an organic and inorganic nature) and recyclability and which also exhibit a high hardness and low elongation.
One possibility of producing a higher degree of hardness of the dried coating layers is to branch the polymer molecules. Branched polyurethane polyureas, such as are described in EP-A 242 731, have such a high hardness that they are used for producing coatings for hard, non-flexible substrates, for example as parquet coatings. When applied in a cosolvent-free manner to glass plates, the satisfactorily adhering coating layers exhibit cracks after drying at room temperature. These coating layers are not strippable as a film. A dispersion produced from EP-A 242 731 is denoted hereinafter as dispersion B.
It has now surprisingly been found that the desired application properties are obtained if at least two mutually miscible, cosolvent-free, aqueous anionic dispersions A and B of polyurethane polyureas are mixed, whose dry films A have a glass transition temperature Tg in the range from xe2x88x9230xc2x0 to xe2x88x9245xc2x0 C. and dry films B have a first Tg in the range from xe2x88x9230xc2x0 to xe2x88x9245xc2x0 C. and a second Tg in the range from +45xc2x0 to +60xc2x0 C., and the mixture of A and B as a dry film has only one Tg in the range from xe2x88x9230xc2x0 to xe2x88x9245xc2x0 C.
It is extremely surprising that a mixture of dispersions A and dispersions B forms coherent, strippable and recyclable films, since the person skilled in the art must have expected that the good adhesion of the dispersion B would also be transferred to the coating composition mixture of dispersion A and B, impeding strippability. This, however, is not the case. With the mixtures according to the invention, high-gloss, highly transparent and hard coating layers are obtained having a high filling capacity and good strippability and recyclability.
The present invention relates to light-stable coating compositions comprising a mixture of at least two cosolvent-free aqueous, anionic dispersions A and B of polyurethane polyureas, wherein polyurethane dispersion A as a dry film has a Tg in the range from xe2x88x9230xc2x0 to xe2x88x9245xc2x0 C. and the polyurethane dispersion B as a dry film has a first Tg in the range from xe2x88x9230xc2x0 to xe2x88x9245xc2x0 C. and a second Tg in the range from +45xc2x0 to +60xc2x0 C., and the mixture of A and B as a dry film has only one Tg in the range from xe2x88x9230xc2x0 to xe2x88x9245xc2x0 C.
The present invention also relates to light-stable coatings applied in the form of a mixture of at least two mutually compatible aqueous dispersions to arbitrary substrates and are dried at temperatures of up to 150xc2x0 C.
The present invention also relates to a process for producing the light-stable coating compositions according to the invention, wherein at least two different cosolvent-free, aqueous, anionic dispersions A and B of polyurethane polyureas are prepared separately and aqueous dispersions A and B are then mixed in weight ratios of 50 to 90, preferably 55 to 85 parts of A to 10 to 50, preferably 15 to 45 parts of B (based on solids).
The present invention further relates to the use of mixtures of the aqueous dispersions A and B for preparing high-gloss, light-stable, water-resistant, solvent-free coatings for protecting vehicles, steel, aluminium and metal objects of all types, glass and plastics of all types, mineral substrates, brickwork or natural stones, for preventing corrosion of ships, bridges, aircraft and railways, and for protecting wood and natural objects and other substrates by dipping, knife coating, casting, spraying, brushing or injection, followed by drying at 20xc2x0 to 150xc2x0 C.
The present invention relates to the use of mixtures of the aqueous dispersions A and B as recyclable strippable coating compositions for the temporary protection of vehicles, railways, ships, furniture, metal objects, mineral objects, glass and plastics objects and other substrates by dipping, knife coating, casting, spraying, brushing or injection, followed by drying at 20xc2x0 to 100xc2x0 C., preferably 20xc2x0 to 80xc2x0 C., by heat or infra-red light, microwave irradiation or sonic irradiation.
The present invention also relates to the use of the used, stripped coatings according to the invention as recycled material, wherein the used, stripped coatings are mechanically comminuted, optionally after prior cleaning, are dissolved, optionally while heating, in acetone, water and neutralizing agents, preferably ammonia, the acetone is optionally distilled off under reduced pressure, and the recovered stripped coating composition is obtained in the form of an aqueous dispersion for renewed use.
The present invention also relates to the use of the used, stripped coating layers according to the invention as recycled material, wherein the used, stripped coating layers are mechanically comminuted, optionally after prior cleaning, and are then compressed in heatable presses under application of temperature and pressure to form polyurethane plates, or the comminuted coating layers are extruded in an extruder under application of temperature, shear forces and conveying, into thermoplastic endless strands, and the resultant strands are granulated by known granulation methods into cylindrical, spherical, lens-shaped or lozenge-shaped granulates.
The present invention also relates to strippable coatings for the temporary protection of motor vehicles, aircraft, steel and aluminium profiles, glass and plastics discs and arbitrary other substrates.
Finally, the present invention relates to the use of the resultant granulates for producing industrial and technical articles as thermoplastic elastomers by further processing in known plastics technology processes, for example by injection moulding, blow moulding, thermoforming, slush moulding or flat extrusion.
Suitable dispersions A for the light-stable coating compositions according to the invention include cosolvent-free, aqueous, anionic dispersions of polyurethane polyureas, whose solids contain the reaction product, present at least partially in the salt form, of
a) an NCO-prepolymer prepared from
i) 20 to 60 wt. % of a diisocyanate selected from aliphatic diisocyanates, cycloaliphatic diisocyanates and mixtures thereof,
ii) 20 to 80 wt. % of a macrodiol having a number average molecular weight of 500 to 10000,
iii) 2 to 12 wt. % of 2,2-bis-(hydroxymethyl)-alkanemono-carboxylic acids, preferably dimethylolpropionic acid,
iv) 0 to 15 wt. % of short-chain diols with a molecular weight of 62 to 400,
v) 0 to 10 wt. % of monohydric alcohols as chain regulators with a molecular weight of 32 to 350,
b) 0 to 15 wt. % of diamines in the molecular weight range of 60 to 300 as chain extenders,
c) 0 to 10 wt. % of chain regulators selected from the group of monoamines, alkanolamines and ammonia,
d) 0 to 3 wt. % of water, and
e) 0.1 to 10 wt. % of neutralizing agents, wherein the preceding percentages total 100% provided that in the prepolymer stage a) the calculated NCO content is 65 to 85%, preferably 75 to 80%, of the theoretical NCO content.
Suitable dispersions B for the light-stable coating compositions according to the invention include cosolvent-free, aqueous, anionic dispersions of polyurethane polyureas whose solids contain the following reaction product, present at least partially in the salt form, of:
a) a NCO prepolymer prepared from
i) 20 to 60 wt. % of a diisocyanate selected from the group of aliphatic diisocyanates, cycloaliphatic diisocyanates and mixtures thereof,
ii) 10 to 80 wt. % of a macrodiol with a number average molecular weight of 500 to 10000,
iii) 2 to 12 wt. % of 2,2-bis-(hydroxymethyl)-alkanemonocarboxylic acids, preferably dimethylolpropionic acid,
iv) 0 to 15 wt. % of short-chain diols and triols with a molecular weight of 62 to 400,
v) 0 to 10 wt. % of monohydric alcohols as chain regulators with a molecular weight of 32 to 2500,
b) 0 to 15 wt. % of diamines and triamines in the molecular weight range of 60 to 300 as chain extenders
c) 0 to 10 wt. % of chain regulators selected from monoamines, alkanolamines and ammonia,
d) 0 to 3 wt. % of water, and
e) 0.1 to 10 wt. % of neutralizing agents, wherein the preceding percentages add up to 100% provided that the branching is achieved with triols and/or triamines, that is not both a iv) and b) may not be zero.
Dispersions A and B contain the components described in more detail hereinbelow; the specific features of the dispersions A and B are disclosed thereafter.
Component a) i) is selected from aliphatic and/or cycloaliphatic diisocyanates, such as isophorone diisocyanate (IPDI), 4,4xe2x80x2-dicyclohexylmethane diisocyanate, 1-methyl-2,4-diisocyanato-cyclohexane and/or 1-methyl-2,6-diisocyanatocyclohexane, 1,6-hexamethylene diisocyanate and/or 1,3-cyclohexane diisocyanate.
The use of small proportions of aromatic diisocyanates such as 2,4- and 2,6-toluene diisocyanate or 2,4xe2x80x2- and 4,4xe2x80x2-diphenylmethane diisocyanate, is also possible.
As component a) ii) macrodiols with a number-average molecular weight of 500 to 10000 are used. These macrodiols are preferably polyester diols obtained by reacting dicarboxylic acids with diols, optionally with the aid of conventional esterification catalysts, preferably by melt condensation or azeotropic condensation at temperatures of 140xc2x0-240xc2x0 C.
Examples of suitable acids or anhydrides include adipic acid, succinic acid (anhydride), maleic acid (anhydride), sebacic acid, azelaic acids, the various commercially available dimeric fatty acids (in hydrogenated and non-hydrogenated form), phthalic acid (anhydride), isophthalic acid, tetrahydrophthalic acid (anhydride), 1,4-cyclo-hexanedicarboxylic acid and hexahydrophthalic acid (anhydride).
Examples of suitable diols are industrially available and include ethylene glycol, 1,2- and 1,3-propanediol, 1,3- and 1,4-butanediol, 1,6-hexanediol, diethylene glycol, dipropylene glycol, neopentyl glycol or mixtures of such diols. Polyester diols of adipic acid, hexanediol and neopentyl glycol are preferred.
Also suitable are polycarbonate diols, polycaprolactone diols, hydroxy-polytetrahydrofurans or hydroxypolyethers based on propylene oxide.
Suitable polycarbonate diols are obtained for example by reacting carbonic acid derivatives including diphenyl carbonate or phosgene with alcohols, preferably diols of the aforementioned type.
The number-average molecular weight of these polyols is between 500 and 10000, preferably between 700 and 4000, and more preferred between 1000 and 2500.
Starting components a) iii) are selected from 2,2-bis-(hydroxymethyl)-alkanemonocarboxylic acids having a total of 5 to 8 carbon atoms, i.e. compounds of formula (I) 
wherein
R represents an alkyl radical with 1 to 4 carbon atoms. 2,2-dimethylolpropionic acid is preferred.
Suitable starting components a) iv) include the previously described short-chain diols of molecular weight 62-400. 1,4-butanediol is preferred.
Suitable starting components a) v) include methanol, ethanol, butanol, hexanol, 2-ethylhexanol, octanol and dodecanol, and alcohols of molecular weight 32 to 350.
Suitable components b) include aliphatic and/or cycloaliphatic compounds having at least two amino groups reactive to isocyanates. Suitable compounds include ethylene diamine, propylene diamine, hexamethylene diamine, isophorone diamine, p-xylylene diamine, 4,4xe2x80x2-diaminodicyclohexylmethane and 4,4xe2x80x2-diamino-3,3xe2x80x2dimethyldicyclohexyl-methane.
Suitable components c) include ammonia, monofunctional amines such as methylamine, ethylamine, n-propylamine, isopropylamine, cyclohexylamine, octylamine, diethylamine, dibutylamine, and amino alcohols such as ethanolamine, diethanolamine and propanolamine.
Suitable as neutralizing agents e) include ammonia, N-methylmorpholine, dimethylisopropanolamine, triethylamine, dimethylethanolamine, methyldiethanolamine, triethanolamine, morpholine, tripropylamine, ethanolamine, diethanolamine, triisopropanolamine and, and N-ethyldiisopropylamine.
In a preferred embodiment components a) i), ii) and iii) are placed in a reactor and reacted under anhydrous conditions in a temperature range of 50xc2x0-1500xc2x0 C., preferably 50xc2x0-110xc2x0 C. The reaction mixture is then cooled and acetone as well as the short-chain diol (iv) and optionally monohydric alcohols (v) are added and the whole is heated until the NCO content of the mixture has fallen to a value of 65 to 85% of the theoretical NCO content. The NCO prepolymer is formed in this way. The reaction mixture is diluted with further acetone and the calculated amount of a mixture of diamine and chain terminatorxe2x80x94dissolved in waterxe2x80x94is added. In this way 90% of the NCO groups of the prepolymer are reacted with the chain extender, the diamine and the chain terminator, the rest will react with the water being present. The remaining isocyanate can be reacted with the water present to form the polyurethane polyurea according to the invention.
The polymer build-up reaction is preferably carried out without the use of catalysts, though it is also possible to use the catalysts known in isocyanate chemistry (for example tertiary amines such as triethylamine, tin compounds such as tin-II-octoate, and dibutyltin dilaurate and other known catalysts).
When no more NCO can be detected (IR measurement) the calculated amount of neutralizing agent, preferably ammonia solution, is added to the reaction mixture so that 50-60% of the carboxyl groups present are neutralized by the ammonia.
The desired solids concentration is adjusted by adding water followed by removal of the acetone by distillation. Polyurethane polyurea dispersions that are obtained according to the process of the invention contain 20-60 wt. % of solids, preferably 30-40 wt. % of solids in water, and their mean particle diameters are 20-1000 nm, preferably 50-500 nm.
The pH of the white, storage-stable polyurethane polyurea dispersions according to the invention is in the range from 6 to 9.
Suitable dispersions B are obtained according to the known processes of the prior art. Methods for producing such branched polyurethane plastics are described for example in EP-A 242 731 (corresponding to U.S. Pat. No. 4,745,151 hereby incorporated by reference). EP-A 269 972 (corresponding to U.S. Pat. No. 4,764,555) hereby incorporated by reference) discloses polyurethane polyurea dispersions modified by monohydric polyether alcohols and neutralized with ammonia. Dispersions B contain branching compounds. Example include triols such as trimethylolpropane and glycerol, or triamines such as diethylenetriamine.
The preferred polyether alcohols are monofunctional, contain ethylene oxide and optionally propylene oxide, are preferably started on n-butanol and have mean molecular weights of 250 to 2500. Since these polyether alcohols act as non-ionic hydrophilic groups, they preferably contain more than 50 wt. % of ethylene oxide in the chain.
Dispersions A and B may be blended with other anionic or non-ionic dispersions. Examples include with polyvinyl acetate, polyethylene, polystyrene, polybutadiene, polyvinyl chloride, polyacrylate and copolymer plastics dispersions.
Dispersions A and B are mixed in a resin solids ratio of 50 to 90 parts of A to 10 to 50 parts of B, preferably 55 to 85 parts of A to 15 to 45 parts of B.
The desired pH of the mixtures may optionally be adjusted with organic or inorganic bases, such as ammonia, alkali metal carbonates, amines or amino alcohols. Organic bases are preferred. 2-amino-2-methyl-1-propanol is especially preferred.
Known additives used in coating composition chemistry, such as pigments, light stabilisers, anti-settling agents, thickeners, surfactants, and defoaming agents, may be used in the formulation of the coating compositions.
The coating compositions are applied by the conventional methods used in coatings technology, i.e. dipping, knife coating, casting, spraying, injection, brushing, painting or rolling.
The coatings according to the invention are water-resistant, transparent, tear-resistant, UV-resistant, temperature-resistant, precipitation-resistant (against precipitations of an organic or inorganic nature) and optionally pigmented coatings that on the one hand adhere to the substrates, and on the other hand can easily be removed by stripping.
The coating compositions serve as strippable coatings for the temporary protection of vehicles, steel and aluminium profiled parts, glass and plastics discs and articles. After application the coated parts are dried at room temperature or at elevated temperatures of up to 150xc2x0 C./(100 ??).
If the polyurethane urea dispersions according to the invention are dried for up to 30 minutes at 140xc2x0-150xc2x0 C. then coatings are obtained that adhere well to the substrates. Drying temperatures above 150xc2x0 C. are also possible, although the use of such high temperatures is in general not economical.
The recycling of the used, stripped coatings is very simple. The stripped coatings layers are mechanically comminuted, optionally after prior cleaning, dissolved in acetone in a reaction vessel, optionally under heating, and optionally filtered after dissolution. The calculated amount of neutralizing agent, preferably ammonia, is added, and the whole is diluted with water to the desired solids content of the aqueous polyurethane polyurea dispersion. Finally, the acetone is optionally distilled off under reduced pressure.
Another method of recycling the used, stripped coating layers is to mechanically comminute the used, stripped coating layers, optionally after prior cleaning, and then press the comminuted material in heatable presses under the application of temperature and pressure to form polyurethane plates. It is also possible to extrude the comminuted coating layers in an extruder under the application of temperature, shear forces and conveying, into endless thermoplastic strands and granulating the resultant strands according to known granulation methods into cylindrical, spherical, lens-shaped or lozenge-shaped granulates. Such granulates are used as thermoplastic elastomers in the production of industrial articles by further processing in known processes used in plastics technology, for example by injection molding, blow molding, thermoforming, slush molding or flat extrusion.